The effect of vertical visual target location on head and neck posture

Twelve participants viewed a visual target placed in 6 vertical locations ranging from 30° above to 60° below horizontal eye level. This range of vertical target location was associated with a 37° change in head orientation, and a 53° change in gaze angle with respect to the head. The change in head orientation was predominantly achieved through changes in atlanto-occipital posture. Consideration of these data in light of preferred gaze angle data, and neck muscle length/tension relationships, suggests that visual targets should be located at least 15° below horizontal eye level.